Multiple coil tubular heating element



June 17, 1952 c. B. BACKER MULTIPLE COIL TUBULAR HEATING ELEMENT 2 SHEETSSHEET 1 Filed Oct. 15, 1949 C. B. BACKER MULTIPLE COIL TUBULAR HEATING ELEMENT June 1 7, 1952 2 SHEETSSHEET 2 Filed Oct. 15, 1949 ww V IN an g an ii all:

R r w MW mm W m 5 .m .m p 17v Z CY B Patented June 17, 1952 MULTIPLE COIL TUBULAR HEATING ELEMENT Christian B. Backer, Ottawa, Ontario, Canada Application October 15, 1949, Serial No. 121,516 In Canada. November 18, 1948 Claims. 1

This invention relates to tubular electric heating elements, and more particularly to that type of element wherein a single tube contains more than one resistance coil.

Such multiple coil tube elements were produced by the applicant some fifteen years ago and were then used for water heaters and other liquid heaters in cases where lack of space prevented the use of the hair-pin type of tubular element. Three types of multiple coil heaters were made at that time, namely a two-coil heater with a return conductor having three terminals at one end of the tube; a one coil heater in which the coil had a return bend inside the tube at one end, which was closed up, so that both terminals came out at the other end of the tube; and a three coil heater for three phase current in which three ends of the coils were joined together inside the element tube at one end, which was closed up, and the other three ends of the coils formed terminals at the other end of the element tube. These multiple-coil tube elements were satisfactory for liquid heaters, that is, for low temperature heaters, but for high temperature work, such as tubular boiling plates, the adjacent heatingcoils would heat each other up to an extremely high temperature and thereby seriously reduce the life of the element, and make it very sensitive to overloads. Nevertheless boiling plates having only one tube with two heating coils beside each other, connected to a return wire inside the tube at one end, and having three terminals at the other end of the tube, have recently appeared on the market. The great advantage of such a design is that it is cheap in production, as compared to boiling plates with two or three tubes.

However, such previously proposed heating elements are subject to at least two disadvantages. One of these is the above-mentioned fact that the two heating coils reach a very high temperature in the region where the coils are nearest to each other. The other very serious disadvantage is that the heat is distributed over the whole surfaoe of the plate even at medium load. This means that with small boiling vessels (say, 4" to 6? diameter) about half the energy is wasted. It must be recognized as a definite requirement that a boiling plate (except the very smallest size, such as a 4 diameter plate) shall have a socalled hot center, when the switch is set at the medium position. When the medium load is distributed over the whole plate it is of substantially no use, since the full load is always required to bring the liquid to the boiling point,

and thereafter the simmering load is sufficient. In other words, the medium load is useful only for rapid boiling in a small diameter vessel, but that is frequently required.

It will further be realized that the design of the one-tube boiling plate now on the market does not provide a plate with three heating coils, which is required in substantially all European countries to attain a reasonably low simmering load. In the United States and Canada the low simmering (keeping warm) load is attained with only two heating coils by employing two voltages on the same boiling plate (115 v. and 230 v.). This arrangement is not available in any European country, and the low simmering load to 200 Watts) can be attained only by providing three element coils in series.

The present invention seeks to overcome these disadvantages, and one of the objects of the invention is to provide a low cost tubular heating element havingat least two heating coils so arranged within a tube or sheath that one of the coils will heat one portion of the tube and another coil will heat the remaining portion. Another object is to provide a multiple coil heating tube wherein the tube or sheath follows the transverse contour of each coil throughout a major portion thereof whereby the heat of the coils is dissipated through the tube with substantial resultant reduction in heating of the coils per so by each other.

The invention contemplates the provision of a heating tube having a plurality of resistance coils therein, one of said coils having a portion extending from one end of the tube to a point intermediate the ends of the tube and a return portion extending from said point to said end of the tube, and another of the coils having a portion extending from the other end of the tube to a point adjacent the intermediate point and a return portion extending from said adjacent point to said other end of the tube.

In other words, the invention includes a tubular heating element comprising a tube havingits ends arranged in adjacent relation, and at least two return-bend heating coils within the tube, one coil havingtwo ends extending to one end of the tube, another coil having its two ends extending to the other end of the tube, the return bend in each coil lying adjacent each other within the tube.

The invention will be described with reference to the accompanying drawings in which:

Figure 1 is a plan view of a boiling plate in accordance with the invention,

Figure 2 is a crosssection of the boiling plate shown in Figure 1,

Figure 3 is a plan view of another form of boiling plate,

Figures 4 to 8, inclusive, are enlarged trans-- verse sections of various alternative forms of tubular heating elements in accordance with the invention,

Figure 9 is a transverse section of a heretofore proposed tubular heating element,

Figure 10 is a plan view of another embodiment of boiling plate in accordance with the invention,

Figure 11 is a cross-sectional elevation of the boiling plate shown in Figure 10.

Figure 12 is a longitudinal sectional elevation of the heating tube shown in Figure 8,

Figure 13 is a plan view of a boiling plate in accordance with another embodiment of the invention,

Figure 13a is a partial sectional elevation of the plate shown in Figure 13.

Figure 14 is a plan view of a water heater, and

Figure 15 is a sectional elevation of a water heater shown in Figure 14.

Referring to Figures 1, 2 and 4, i is a boiling plate having a single tubular element 2 supported on a spider 3. The element is arranged with a plurality of substantially concentric convolutions 4 and the ends of the element extend laterally from the plate in the same plane for connection to a terminal box. The element comprises an outer tube or sheath 5 containing two resistance coils 6 and 'i embedded in suitable insulation Coil 6 extends from one end of the tube through the outer convolution of the element to a point two ends of coil 1 thus extend to the other end H of the tube, where they are provided with terminal pins 12. The ingoing and return sections of each coil lie in laterally spaced relation within the tube as clearly shown in Figure 4. In the boiling plate shown, with both coils 8 and l on high load, maximum heating is provided, distributed over the entire plate. On medium load coil 1 only may be energized to provide the desired hot center. With both coils in series, the simmering load will be distributed over the entire 1" plate, which is the desired distribution for simmering.

An alternative design of two-coil tube is shown in Figure 5, which design permits the use of a longer tube in a specified diameter of boiling plate. The tube 13 contains two coils 14, each of which has its return section l4 located underneath the primary section and is thus remote from the cooking utensil. It is desirable, in

this embodiment, that the return section be stretched more than the primary section, 1. e., be provided with less turns, per inch, so that the heat released on the underside of the tube will not be more than, say, one-quarter or one-third,

of the amount of heat generated in the top (pri- .L

mary) section of the coil. It will be understood that when the energy in the return section of the coil is only or of the total energy of the coil, heating up of the primary section by the no objectionable excess temperature in the coil.

Referring to Figures 3 and 6, a one-tube boiling plate with three heating coils is shown, which is suitable for use in countries where two voltages are not available. The tube 15 contains two main heating coils i6 and 11 arranged in a manner similar to that described with reference to Figure 1. Thus each coil has a return bend 16 or I? with respective terminals l8 and 18 at the ends of the tube so that the inner convolutions of the element may be heated separately from the outer convolution. The tube also contains a third or simmering coil [9, which extends throughout the length of the tube with a terminal 29 at each end of the tube. The coil i9 is of much lower wattage, say, to 300, than that of the main coils l6 and H. To attain the lowest heat (the keeping warm heat) all three heating coils are connected in series (with a standard Q-heat, 'I-heat or 4-heat switch), and the heat is then distributed over the whole surface of the plate, which is the desired arrangement for simmering and for keeping dishes warm. The three coils may be arranged in laterally spaced relation as shown in Figure 6, or they may be arranged with the simmering coil l9 below the main coils l5 and IT, as shown in Figure 7, the latter arrangement requiring a differently shaped tube 2!.

One of the greatest difliculties in the production of tubular boiling plates with three heating tubes (one of which must have very low wattage to produce a simmering load of not more than or watts) has been the handling of the extremely fine resistance wire required for an element of 200 to 300 watts for 230 volts or higher, particularly since the low wattage tube must be always of very short length, because there is no room for a long tube. It will be readily understood that the life of such a fine wire is likely to be limited. The simmering tube in the threetube boiling plate has been always therefore the weakest link in the three-tube type of plate. This difficulty has been overcome in the three-coil tube element of the present invention, since the simmering coil in it extends the full length of the tube, which provides space for a comparatively large wire, even though the loadis only 200 or 150 watts, and the voltage may be 250.

Referring to Figures 10 and 11, a boiling plate 22 is shown which may be of extremely small diameter, say, 3 to 3% inches, by arrangement of the tubular element, which is similar to element with the tube 23 thereof on edge. As shown, the sections of each coil 24 will then lie in vertically spaced relation. There has always been a great need for such a small diameter plate for rapid boiling of small diameter vessels, such as coffee percolators, for which even the standard six inch plate is too large and too slow. While it would have been possible heretofore to make such a plate with only one heating coil, that solution is not satisfactory, because at least one, or preferably two, simmering loads are required to continue the boiling operation after the boiling point is reached. By using one section of coil of, say, 1000 watts, at the top edge of the tube, and another section of, say, 200 watts, at the bottom edge, one can obtain loads of 1200, 200 and 167 watts, with the ordinary three-heat series-parallel switch. This provides a most satisfactory regulation for such a small plate, and the plate will boil liquids in a vessel of, say, four inch diameter, about twice as fast as other boiling plates return section will be very slight and will cause 7 heretofore proposed.

In Figure 8 is shown a four-coil tubular element arrangement, wherein three main coils 25, 26 and 21 and a low temperature coil 28 are arranged within a sheath 29.

Figure 12 illustrates an arrangement wherein a tubular sheath 30 is similar in cross-section to sheath 29 and contains a low temperature coil 3| extending from end to end of the tube and connected to terminals 32 at each end of the tube, a second coil 33 extending from end to end of the tube but having a substantially straight portion 33' whereby it heats only portion 34 of the tube, and a third coil 35 extending from end to end of the tube but having a substantially straight section 35' where it heats only portion 36 of the tube. Coil 35 is connected to terminal 32 at one end of the tube and to terminal 3! at the other end. Coil 33 is connected to the other terminal 32 and to terminal-38 at the other end of the tube. It will-thus be understood that the hot center design of boiling plate may be attained with the element shown in Figure 12, although the coils pass through the entire length of the sheath.

Figures 13 and 1311 show a boiling plate 39, which utilizes a tubular element, similar to I5, but wherein the terminals and M are arranged at the center of the plate. The standard European design of boiling plate has the plug-in terminal pins arranged underneath the plate in the center, which makes the application of tubular elements extremely difiicult in such plates, because of lack of space (head room) in the standard design. The attainment of very low simmering loads in such plates has so far been extremely difficult, if not impossible. This problem may now be solved with the type of tube elements herein described. The plate 39 may have one simmering coil of 200 watts, an inner coil of 900 watts or more, and an outer coil of 900 watts or more, which, with a multiple switch, will provide several low loads, the lowest one of which will be 137 watts. As shown, one end of the tube extends downwardly to the terminal 40 from the plane of the plate, and the other end of the tube, which has a portion 48 extending below the convolutions of the element to the center of the plate, extends upwardly to the plane of the plate, as indicated at 49, and then downwardly to the terminal 4 l.

A similar layout of the tube may be used with a two-coil tube having one large coil of, say 1800 watts, and one simmering coil of 200 watts. Both of these coils would then have to extend the full length of the tube. ment the hot center feature cannot be attained, but satisfactory simmering loads may be had with the standard three-heat series-parallel switch.

Figure 9 illustrates in cross-section a heretofore proposed design of multiple coil tube. A tube 42 has two laterally disposed coils '43 of the same wattage, the inner end of each coil being connected to a return wire 44. The tube or sheath 4'2 surrounds only about 60% of the circumference of each coil. The inner portions of the circumference of both coils heat each other up, and the heat cannot readily be transmitted to the sheath through the heavy insulation covering the inner portions of the circumferences of the coils. It has been said that the heating coil itself will transmit the heat from its inner half to the outer half of its circumference, but this statment is only partially true, as a simple calculation of the heat transfer in the resistance With such an arrangecell will show. The fact remains that the inner halves (more or less) of the circumferences of the coils will, under full load, operate at so much higher temperature than the outer halves that it cuts down the overload capacity of the plate (expressed as a percentage of the normal load) to a fractionof what it would be in a tube element with a centrally located heating coil, running at an even temperature.

It will be observed that each of the tubes or sheaths shown in Figures 4 to 7, inclusive, are shaped in crossfsection to conform to as great an extent as possible with the contour of the enclosed coil. n Thus, such outer tubes surround the coil to a much greater extent than is the cause than is the case in respect of sheath 42 in Figure 9. While in the latter design not more than about 60% of the circumference of the coil is surrounded by the sheath, more than of the circumference of the coils is surrounded in the forms of the present invention. This makes a deciding difference in the maximum temperature of the heating coil.

Referring to Figures 14 and 15, a one-tube water heater of hair-pin shape is shown, having a sheath 45 containing two heating coils 46 extending from end to end of the tube and connected to terminals 41 at each end. The sheath has the same cross-section as that shown in Figure 4. The two heating coils may be of equal wattage or, in case a very low keeping warm load is desired, one coil may be of much lower wattage than the other.

It will be obvious that the invention may be applied to room heater tubes of varying shape, wherein a single tube may contain two heating coils each running only to the center of the tube and returning to the same end of the tube, so that full temperature radiant heat may be obtained from one half of the tube, when the switch is set at medium heat.

The invention may also be applied to other electrical heating means such as kettle elements, oil heaters and other industrial heating elements in which it is desirable to attain heat regulation in a plurality of steps without the use of more than one element tube.

The electrical insulation required in all the tube elements described may be formed around the resistance coils in any suitable manner. For instance, the coils may be embedded in magnesium hydroxide in the manner defined in my copending application for patent, Serial No. 663,-

201, filed April 18, 1946, now Patent No. 2,490,611

December 6, 1949.

I claim:

1. A tubular heating element comprising an outer tube, at least two heating coils arranged inside the tube, each said coil having separate terminals and being in disconnected relation to the other coil, one coil having a heating section extending throughout one longitudinal portion only of the tube and arranged to heat the latter portion only, and the other coil having a heating section extending throughout the remaining longitudinal portion only of the tube and arranged to heat the latter portion only.

2. A heating element comprising an outer tube, and a plurality of resistance coils therein, each said coil being in disconnected relation to the other coils, one of the coils having a section extending from one end of the tube to a point intermediate the ends of the tube and a return section extending from said point to said end of the tube, and another of the coils having a section extending from the other endof the tube to a point adjacent said intermediate point and a return section extending from said adjacent point to said other end of the tube.

3. A tubular heating element comprising a tube having its ends arranged inadjacent relation, and at ,least two return-bend heating coils within the tube, each said coil being in disconnected relation to the other coil, one coil having its two ends extending to one end of the tube, and the other coil having its two ends extending to the other end of the tube, the return bend in each coil lying adjacent each other within the tube.

4. A tubular heating element as per claim 2 having a third heating coil of low load, said coil running the full length of the tube and having one terminal at each end of same, to provide heat over the whole tube for simmering.

5. An electric boiling plate comprising a con REFERE CES CITED The following references'are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,042,203 Backer May 26, 1936 2,051,637 Goldbert et a1. Aug. 18, 1936 2,455,186 McCormick Nov. 30, 1948 2,456,343 Tuttle Dec. 14, 1948 2,506,554

Tuttle May 2, 1950 

